This invention relates generally to integrated optics and, more particularly, to optical modulators and methods of modulating light propagating in a waveguide.
In integrated optics, thin film technology is employed in optical circuits and devices to achieve more efficient, more economical and minute circuitry. In integrated optic waveguides, modulators and the like, a thin optical waveguide in the form of a light-propagating thin film, which may be only a few microns in thickness, is supported on a substrate. In order to propagate light, the film must have an index of refraction greater than that of the substrate and any other material in contact with the film, such as air. When this condition occurs, light entering the film will be reflected between the film surfaces and retained in and guided along the film.
It is advantageous to modulate the light propagating through the waveguide film in some aspect, for example, intensity, mode, frequency, etc. Such modulation varies some characteristic or property of the light that is discharged from the waveguide film so that it may carry information. Thus, in integrated optics, modulators are valuable in many applications.
Several useful types of optical modulators are presently known. One such type achieves optical modulation by mode defraction. Mode defraction is accomplished by passing acoustic sound waves, either bulk or sheer, through the waveguide. Alternatively, when the waveguide is a piezoelectric material, mode defraction is accomplished by passing an electric current through the waveguide. The current causes sufficient movement of the waveguide to achieve mode defraction.
Another presently known type of modulation is accomplished by changing the optical path length of an optical fiber. Such a path length can be accomplished by compressing the fiber.
It is also known to accomplish modulation of light propagating in a waveguide by changing the refractive index of the guide material. This is sometimes accomplished, for example, with interdigitated electrodes. The interdigitated electrodes can be arranged to form a diffraction grating for coupling light into and out of waveguides.
Another known method of modulating light propagating in a wavelength is to change the index of refraction of a liquid crystal material overlying the waveguide. The change in refractive index is accomplished by changing the crystal orientation from the direction of propagation to normal thereto.
A more recent discovery furnishes modulation of light propagating in an elastomeric waveguide of a given cross-section by changing the cross-sectional dimension of the waveguide. The change in dimension effects modulation by mode termination. Modulation is accomplished by impressing an electric field across the elastomeric waveguide. The field is established between electrode means placed on either side of the elastomeric waveguide.
Deformation of an elastomeric waveguide is known to produce effective modulation of propagating light. However, improvements are sought which would optimize this method of modulation. Improvements are sought especially in the areas of increased frequency and reduced deformation to accomplish modulation.